Field of the Invention
The present invention relates to a magnetic carrier, a two-component developer, and a developer for replenishment for use in an image forming method for visualizing an electrostatic image by electrophotography, and an image forming method involving the use of the magnetic carrier, the two-component developer, and the developer for replenishment.
Description of the Related Art
In typical electrophotographic image forming methods, electrostatic latent images are formed on an electrostatic latent image bearing member using various means. Toner is applied to the electrostatic latent images, and the electrostatic latent images are developed. The development is widely performed using a two-component development system. In the two-component development system, carrier particles called a magnetic carrier are mixed with toner, and the toner bears an adequate amount of positive or negative charge due to triboelectric charging. The electric charge is used as driving force for the development.
In the two-component development system, the magnetic carrier has functions of agitation, conveyance, and charging of a developer. Thus, the functions of the magnetic carrier can be clearly separated from the functions of the toner. Thus, the two-component development system has the advantage that the performance of the developer can be easily controlled.
With recent technological advances in electrophotography, there is a growing demand for higher-definition apparatuses and higher stability of image quality as well as higher-speed and longer-life apparatuses. In order to meet such a demand, there is a demand for a higher-performance magnetic carrier.
Reduction in density variation and, in the case of full color, color variation during long-term use is proposed in Japanese Patent Laid-Open No. 4-93954. A carrier described in Japanese Patent Laid-Open No. 4-93954 is characterized in that a magnetic core material of the carrier has concavities and convexities, and the magnetic core material coated with a resin has uncoated convexities. Although this can improve the density variation and color variation, magnetic carrier particles having a high specific gravity impose a load on toner in recent high-speed copying, and the developer has a short lifetime. Thus, the image quality and adaptability to environmental changes must be further improved.
A magnetic carrier that contains a porous magnetic core having pores and a low specific gravity has been proposed in Japanese Patent Laid-Open Nos. 2012-173315, 2006-337579, 2009-175666, and 2011-158830, and Japanese Patent No. 4898959). Such a magnetic carrier can improve the lifetime of the developer, fogging, carrier adhesion, image-density irregularities, and resistance to leakage. However, such a magnetic carrier causes another problems, such as blank dots or coarseness. Thus, there is an urgent need for the development of a magnetic carrier and a two-component developer that can solve these problems, and an image forming method involving the use of the magnetic carrier and the two-component developer.